Crosslinkable vinyl ester copolymers are polymers based on ethylenically unsaturated vinyl ester monomers and on other ethylenically unsaturated monomers having additional functional groups which, directly or indirectly after transformation, have suitability for the crosslinking reaction. Vinyl ester copolymers are usually prepared via free-radical-initiated polymerization, by the emulsion polymerization process.
Crosslinkable vinyl ester copolymers are used in various application sectors. By way of example, JP-A 04325531 describes the use of ethylene-vinyl acetate-glycidyl methacrylate terpolymers with from 2 to 20% by weight content of glycidyl methacrylate in protective films of solar cells. EP-A 0897376 and U.S. Pat. No. 4,716,080 propose vinyl acetate glycidyl methacrylate copolymers as size for glass fibers. JP-A 08221738 mentions vinyl chloride-vinyl acetate-glycidyl methacrylate copolymers inter alia as coating compositions for magnetic tapes.
GB-A 1456412 describes terpolymers based on vinyl acetate, on (meth)acrylic esters, and on from 0.1 to 2% by weight of ethylenically unsaturated epoxides, these being converted into pressure-sensitive adhesives (also known by the abbreviation PSA), via hardening with phosphoric acid or with phosphoric esters. U.S. Pat. No. 3,579,490 describes copolymers which can likewise be used as PSA and which are obtained via the solution polymerization or emulsion polymerization of ethylenically unsaturated monomers, such as (meth)acrylic esters and from 0.5 to 15% by weight of, for example, glycidyl crylate or allyl glycidyl ether, and also, if appropriate, vinyl acetate and/or acrylic acid. The Tg of the copolymers is from −15 to −65° C. Self-crosslinking copolymers are described in U.S. Pat. No. 3,317,453. These are obtained via solution polymerization of vinyl acetate with 5 mol % of, respectively, acrylic acid and glycidyl methacrylate, and can be crosslinked in the presence of a catalyst, for example a titanium species, within a period of 5 minutes at 90° C. to give a film.
EP-A 1682591 discloses soluble vinyl polymers composed of monounsaturated monomers and of polyunsaturated monomers, where the monomers are intended to be insoluble in organic solvents. Cyclodextrins are used to form complexes with the polyunsaturated monomers, which are then copolymerized with the monounsaturated monomers.
DE-A 1932715 discloses vinyl polymers which were obtained via polymer-analogous reaction of partially hydrolyzed polyvinyl acetate with acyl halides of acrylic acid derivatives, where from 20 to 95% of the hydroxyl groups were reacted and the resultant vinyl polymers contain from 0.3 to 7.0 unsaturated acid units per 1000 molecular weight units. However, the crosslinkable, ethylenically unsaturated groups have direct bonding by way of an ester group to the main chain of the vinyl polymers, and are thus difficult to access for crosslinking using ethylenically unsaturated groups of other vinyl polymers, with a resultant adverse effect on the crosslinking rate. The vinyl polymers are cured on phosphatized steel, using electron beams, together with (meth)acrylates or styrene, as a constituent of paint compositions.
EP-A 0506703 describes crosslinkable copolymers which are obtainable via polymer-analogous reactions of suitably functionalized vinyl ester-vinylaromatic copolymers with ethylenically unsaturated, functionalized monomers. The resultant crosslinkable copolymers have molar masses Mn of from 1500 to 6000 g/mol and are suitable by way of example for use in coating compositions for repair paints for motor vehicles. However, copolymers with such low molar masses Mn often do not have the mechanical properties desired in many applications, examples being high abrasion resistance, high mechanical flexural and tensile strength, or high elasticity, and have an increased tendency toward migration in coatings. The vinyl ester-vinylaromatic copolymers moreover comprise very large amounts of unpolymerized monomers (residual monomers), these being markedly above 5% by weight, based on the vinyl ester content of the copolymers. When the copolymers are used by way of example in the production of coatings, the residual monomers can lead to flow problems and moreover can cause pollution of the environment with volatile organic substances.